Photolithography is commonly used to make miniaturized electronic components such as integrated circuits in semiconductor manufacturing. In a photolithography process, a layer of photoresist is deposited on a substrate, such as a silicon wafer. The substrate is baked to remove any solvent remained in the photoresist layer. The photoresist is then selectively exposed through a photomask with a desired pattern to a source of actinic radiation. The radiation exposure causes a chemical reaction in the exposed areas of the photoresist and creates a latent image corresponding to the mask pattern in the photoresist layer. The photoresist is next developed in a developer solution to remove either the exposed portions of the photoresist for a positive photoresist or the unexposed portions of the photoresist for a negative photoresist. The patterned photoresist can then be used as a mask for subsequent fabrication processes on the substrate, such as deposition, etching, or ion implantation processes.
Advances in semiconductor device performance have typically been accomplished through a decrease in semiconductor device dimensions. The demand for ever smaller semiconductor device has made it necessary to use photolithographic techniques using imaging lights of shorter wavelengths such as 300 nm or less. However, the use of lights of shorter wavelengths for imaging has resulted in increased back reflection from substrates which are detrimental to the lithographic performance of photoresists.
To reduce the back light reflection from highly reflective substrates, prior art processes have typically used a highly absorbing bottom antireflective coating, generally referred to as BARC. A BARC is applied to a substrate and then a photoresist is deposited on top of the BARC layer. Most BARCs known in the prior art are designed to be removed by dry etch. That is, after the photoresist is pattern-wise exposed and developed to form patterned structures in the photoresist, portions of the BARC not covered by the photoresist are then etched away, thereby transferring the patterned structures to the BARC layer. The patterned structures in the photoresist and BARC layers are further transferred to the substrate by removing or by ion implanting portions of the substrate not covered by the photoresist and the BARC. However, dry etch removal of the BARC often causes thinning of the photoresist layer. Thus, if the etch rate of the BARC material and that of the photoresist are not well matched, the patterned structures in the photoresist may be damaged or not properly transferred into the substrate. In addition, the dry etch process may also cause damage to the substrate which will affect the performance of the final device.
Damage to the substrate during dry etch removal processes are especially detrimental to ion implant lithography. Historically, ion implant lithography has avoided the use of BARCs due to the need to implant species such as Arsenic (As), Boron (B) and Phosphorous (P) directly into the silicon surface of a semiconductor substrate. The dry etch processes used to remove a BARC layer could damage the silicon surface, usually by means of oxidation of the silicon surface. However, if the BARC layer is not removed completely prior to ion implanting, the BARC would serve to impede the implant species, causing variation in doping levels that would be harmful to device performance and reliability. On the other hand, it would be desirable to implement a BARC film in order to improve line-width control over the wafer topography which is normally present at the implant mask lithography step, and also to avoid possible resist residues related to the topography or interactions between the resist and the substrate.
Developable bottom antireflective coating (DBARC) materials have recently been introduced as an attempt to provide a film interposed between the photoresist and the substrate to act as an anti-reflective layer (for example, U.S. Pat. Nos. 6,844,131, 7,261,997, and U.S. Patent Application 2007/0243484). Unlike traditional BARC materials, DBARCs can be removed during the resist develop stage, thereby eliminating the dry etch removal step. While the DBARC materials show great promise for being used in ion implant lithography, they often exhibit residues which can block the implant species and degrade the devices. Thus, it is desired to develop processes to remove residues from a patterned substrate in conjunction with the use of DBARC materials in a photolithographic process.